1.9/x+x=6,x^2+9=6x,x^2-6x+9=0,(x-3)^2=0,x=3.
2.(x+1)/x + 2x/( x+1)= 3
两边同乘以x（x+1)
2x^2+(x+1)^2=3*x*(x+1)
2x^2+x^2+2x+1=3x^2+3x
x=1